The present invention relates to a thrust regulator for use with a container having gas under pressure. This thrust results from the pressure which acts upon the surface of a medium in the interior of a container, for instance an aerosol can, in order to keep the flow of this medium per unit time approximately constant during the ejection of this medium from the container. This is in spite of a pressure drop proportional to the amount of the ejected medium, when the pressure is generated by a pressure gas such as air or nitrogen.
Many countries prohibit the use of FREON-type chlorofluorocarbons as propellants in order to contribute to the protection of the ozonosphere shielding our planet against excessive ultra-violet radiation.
Since this prohibition went into effect, mixtures of propane and butane or dimethyl ether have been increasingly used as propellants.
Just as FREON is detrimental to the environment, propanebutane mixtures and dimethyl ether are dangerous because they constitute an explosive hazard.
The use of CO.sub.2, N.sub.2, N.sub.2 O or simply compressure air are tried as propellants. Their use, however, has the disadvantage that during ejection of the product from the container a pressure drop occurs due to the increasingly large volume that remains in the container and which is proportional to this increase in volume. Therefore, the pressure drop causes a decrease of the amount ejected per unit time and when the product is being sprayed the size of the droplets increases at the same time which means that the spray becomes too wet and hence unusable. Moreover the use of CO.sub.2 and N.sub.2 O must be avoided, because these gases are partly absorbed by the product to be sprayed and are therefore ejected with the product, which causes a residual flow in the form of drops after the closure of the valve. This problem can partly be solved by the use of a spary nozzle which the inventor of the present invention describes in his U.S. Pat. No. 4,260,110, and which allows an atomization of products at low mechanical pressure, that is to say without any known propellant gas. These products, through their force of expansion when coming into contact with the air pressure, atomize the droplets as soon as they are released from the nozzle. In the case of this spray nozzle it is only the mechanical breakup which guarantees a satisfactory atomization at a mechanical pressure below 2 bar.
When, however, this spray nozzle is used with aerosol cans using compressed gases as propellants, there occurs a high flow rate per unit time during fine atomization. When the can is filled completely and under high pressure there occurs a low flow rate per unit time during atomization which is still fine when the pressure decreases due to the discharge of the product.
In order to solve this problem of variable flow rates depending on the pressure drop within the can, the present inventor proposes in his European Patent Application No. 81902294.8, "Schubregler zur Verwendung im Inneren von unter Gasdruck stehenden Behaltern", a thrust regulator by means of which the released amount of the medium per unit time being expelled from the container is at least approximately held constant despite the pressure drop becoming effective in the interior of the container. In a discharge channel there is a differential piston, the size of which is provided in such a ratio to the discharge channel that a minimum opening for the escape of the medium is retained during the whole ejection phase. The differential piston has different dimensions at the ends of the surfaces, the larger surface being located opposite to the flow of the medium. The differential piston rests upon a spring which is adjusted in such a way that it is compressed at a certain pressure within the container so that the differential piston takes a first end position, through which it decreases the size of the opening area of the discharge channel to a minimum, and that the spring loses tension proportionally to the pressure drop due to the discharge of the medium from the container and thus shifts the differential piston in such a way that the opening of the discharge channel increases gradually until the piston has reached a second end position as soon as a certain minimum pressure has been reached in the container. The shape of the piston in comparison to that of the discharge channel is chosen in such a way that an at least approximately constant sum of the multiplied pressures in the container is guaranteed through the remaining opening.
Each of the embodiments proposed in European Patent Application No. 81902994.8 has shortcomings and disadvantages such as: too high a permeability to steam pressure of the membranes; too high a price for the injected parts made of synthetic materials due to the pressure required; jerky regulation; and consequently jerky atomization due to an axial to-and-fro movement of the differential piston.